After adding a new instance to a node, when running Instance Configuration, the following errors appear:
1. Go to your SQL Server directory, e.g: D:\Program Files\Microsoft SQL Server\MSSQL10.VCF\MSSQL\Binn\slssqlmaint.exe
2. Rename this file to: slssqlmaint.exe.old
3. In the same directory, if you have the file 'xpSLS.dll', rename this to: xpSLS.dll.old
4. Now run Instance Configuration again.
5. Verify the backups work.